The sources said Monday Mr. Andropov had sent two messages signaling this support: one to the PLO leader, and the second to Syrian President Hafez Assad, currently Moscow's most important Arab ally.

The reported messages followed evident friction between the Kremlin and Mr. Arafat in past months over his avowed interest, however hedged and conditional, in a United States peace plan for the Mideast.

An Arab diplomat said, ''My understanding is that the message called on Assad to refrain from support for any of Arafat's rivals, on the grounds that now is not the time to settle scores.''

Meanwhile, the second in command in Arafat's Fatah guerrilla group is meeting with Soviet officials in Moscow on a visit due to end June 7. Arab sources say signs are that the official, who goes by the nom de guerre Abu Iyad, has also been apprised of Soviet support for Arafat's leadership.

Yet at this writing, the Kremlin has made neither of the reported Mideast messages public, even though the PLO news agency, Wafa, reported Saturday what it termed a message of support from Andropov for Arafat.

Soviet sources were not immediately available for comment on the reported Andropov messages.

But a senior official, speaking generally of the Mideast situation in an interview June 1, said: ''I assume Israel is very happy that the Syrians are not withdrawing from Lebanon (since Israel itself will then not pull out); and that the US is happy the Palestinians are fighting'' among themselves.

Meanwhile, diplomatic activity on another Mideast front - the Iran-Iraq war - has reportedly brought a rare message from Saudi Arabia's traditionally pro-Western leadership to the Kremlin.

An Arab source here reported Monday that ''between a month and six weeks ago'' Saudi King Fahd sentAndropov a ''message on the Iran-Iraq war.''

The source did not say how the message was relayed - Saudi Arabia has no embassy here. He said he had no knowledge of the exact contents of the message but assumed the Saudis sought possible Soviet influence on Iran to come to the bargaining table with Iraq. A similar private appeal from Iraq last year had no visible effect in Tehran.

Some Arab diplomats saw the message as part of an atmospheric thaw between the Saudis and Moscow - in line with a visit last year by the Saudi foreign minister as part of an Arab League delegation. But the diplomats cautioned that they saw no sign yet of any move by Saudi Arabia to renew formal diplomatic ties with Moscow, cut for decades, or significantly to tilt away from the Western world.

Saudi Arabia and other Gulf states have poured huge sums into Iraqi coffers to fund a war Iraq seems increasingly eager to wind down.

Arab sources here said they had no confirmation of Western diplomatic rumors that the Fahd message had also raised the issue of world oil prices.

Reports of the Fahd message come as Kremlin stock in Tehran seems to have reached a new low. Iran recently arrested the leadership of its pro-Moscow communist party and expelled 18 Soviet officials.

Moscow seems so far to have limited itself to some sharp words in response to the expulsion, and some Western diplomats suspect the Kremlin is leery of further jeopardizing its position with neighboring Iran.

Moscow has already quietly resumed some arms shipments to Iraq, abandoning virtual neutrality in the early stages of the conflict, and the Soviet news media had hinted the Kremlin felt increasingly that Iran was the main culprit in prolonging the Gulf war.

Arab sources say the Andropov message to Syrian President Assad, meanwhile, asked also that Damascus offer asylum for exiled Iranian communists. Syria is among the few Arab states to have good relations with Iran.